Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
Unit 3
Chapter 4 Section 4
Solving Proportions
Objective: To solve proportions using unit rates, mental math and cross
products
There are more than one way to solve proportions. In this section, we are going
to solve proportions using unit rates, mental math and cross products. You can
choose which way you like the best, but in certain circumstances you may want to
use one over another.
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
There are many real­life applications for proportions. Can you name a few?
Medicine dosages are frequently related to the weight of the patient, so the dosage must be increased proportionally to weight.
Recipes or formulas may be increased or decreased by using proportions.
Maps, blueprints, and scale models. An appropriate ratio, or scale, is chosen. Large objects or areas can then be shown in a considerably smaller size or space. Movies frequently use scale models of ship, planes, buildings. Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
Examples:
Using Unit Rates
1) You know the price of six oranges, but you need eight. Step 1: Find the unit rate
2.34 dollars
6 oranges
=
6 for $2.34
Step 2: Multiply to find the cost of 8 oranges
2) Postcards cost $2.45 for 5 cards. How much will 13 cards cost?
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
Using Mental Math
3) Solve each proportion using mental math.
a) z = 21
12 36
b)
8 = n
10 40
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
Using Cross Products
4) Solve each proportion using cross products.
a) 25 15
=
38 x
c)
16 d
=
30 51
b) 12
15
d)
= x
21
20 110
=
35 m
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
December 10, 2015
Application:
Write and solve a proportion for each situation.
5) If 12 roses cost $21.96, what is the cost of 5 roses?
6) If 3 onions weigh 2.25 lb, how much do 10 onions weigh?
7) Franklin D. Roosevelt was elected president in 1932 with about 22,800,000 votes. The ratio of the number of votes he received to the number of votes the other candidates received was about 4 : 3. About how many votes did the other candidates receive?
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
Challenge
1) You estimate you will take 75 min to bike 15 mi to
a state park. After 30 min, you have traveled 5 mi.
Are you on schedule?
2)
4) 5) 6)
7)
n+2
= 7
8
4
3)
x+4 = x+20
15
45
December 10, 2015
Unit 3 Chapter 4 Section 4 Solving Proportions.notebook
Homework
Practice Worksheet 4­4
December 10, 2015